Sleep Supplements Explained: The Science of Melatonin, Magnesium, and Glycine

On the road to better sleep quality, many cyclists consider using sleep supplements. The choices on the market are dizzying, from melatonin to various herbal formulas. Which ones are actually backed by science? Which might just be a placebo effect? More importantly, which are safe for athletes? Let’s take a science-based, in-depth look at the three sleep supplements most worth paying attention to.

Melatonin

What Is It?

Melatonin is a hormone naturally secreted by the pineal gland in darkness. Its primary function is not to “put you to sleep,” but to tell the body “it is now nighttime, time to prepare for sleep.” It is a timing signal, not a sleeping pill.

Mechanism of Action

• Lowers core body temperature by acting on MT1 and MT2 receptors in the brain
• Reduces alertness in the nervous system
• Regulates the phase of the circadian rhythm (phase-shifting)
• Has mild antioxidant effects

Scientific Evidence

Situations where it works:

• Jet lag adjustment: This is melatonin’s strongest indication. Multiple meta-analyses confirm that taking it before bedtime at the destination time speeds up clock adjustment
• Difficulty falling asleep: Can shorten sleep onset time by an average of about 7-12 minutes
• Daytime sleep for night-shift workers: Helps with falling asleep at non-standard times

Situations with limited effect:

• Maintaining sleep (the problem of waking up in the middle of the night)
• Increasing deep sleep duration
• Improving sleep quality for those who already have good sleep habits

Guidelines for Athletes

Dosage:
This is the part most people get wrong. Commercial melatonin products typically contain 3-10mg, but research shows that lower doses are actually more effective:

• Physiological dose: 0.3-0.5mg (mimics the body’s natural secretion level)
• Pharmacological dose: 1-3mg (for stronger needs such as jet lag adjustment)
• Common overdose: 5-10mg (may cause counterproductive effects, such as grogginess or headache the next day)

It is recommended to start with 0.5mg and gradually increase if the effect is insufficient.

Timing:

• General sleep aid: 30-60 minutes before bedtime
• Jet lag adjustment: 1-2 hours before bedtime at the destination time
• Avoid taking it after 3 a.m. (it will interfere with waking up in the morning)

Precautions:

• Melatonin is a prescription drug in Taiwan, requiring a physician’s prescription
• Not recommended for long-term daily use; continuous use should not exceed 2-4 weeks
• May affect the balance of certain hormones (long-term safety data is still insufficient)
• Not on the WADA prohibited list, but some competitions may have additional regulations

Magnesium

What Is It?

Magnesium is the fourth most abundant mineral in the human body, involved in more than 300 enzymatic reactions. For athletes, magnesium is not only related to sleep but is also a key element in muscle contraction, energy metabolism, and nerve function.

Why Are Athletes Prone to Magnesium Deficiency?

Endurance athletes are a high-risk group for magnesium deficiency:

• Sweat loss: Each liter of sweat contains 5-15mg of magnesium; a single long ride may result in a loss of 100-200mg
• Increased urinary excretion: Kidney magnesium excretion increases after high-intensity exercise
• Increased demand: Energy metabolism during exercise requires more magnesium
• Insufficient dietary intake: Magnesium content in refined diets has been declining year by year

An estimated 50-70% of people consume less magnesium than the daily recommended amount, and the proportion among athletes may be even higher.

Magnesium’s Sleep Mechanisms

1. GABA receptor activation: Magnesium is a natural cofactor for GABA (gamma-aminobutyric acid) receptors. GABA is the brain’s primary inhibitory neurotransmitter, responsible for “switching off” wakefulness signals
2. Lowering cortisol: Magnesium helps regulate the HPA axis (hypothalamic-pituitary-adrenal axis), lowering stress hormone levels
3. Muscle relaxation: By regulating calcium ion channels, it helps muscles return from a contracted state to a relaxed state
4. Melatonin synthesis: Magnesium is a necessary cofactor in the melatonin synthesis pathway

Different Forms of Magnesium

Not all magnesium supplements are the same. Different forms of magnesium have different absorption rates and specific effects:

Form of Magnesium	Absorption Rate	Characteristics	Sleep Effect
Magnesium Glycinate	High	Glycine itself also has a relaxing effect	★★★★★
Magnesium L-Threonate	High	Can cross the blood-brain barrier	★★★★☆
Magnesium Taurate	High	Additional cardiovascular benefits	★★★★☆
Magnesium Citrate	Medium-high	Lower cost	★★★☆☆
Magnesium Oxide	Low	Cheapest but poorly absorbed	★★☆☆☆

Recommendation: Magnesium glycinate is the first choice for sleep purposes, because glycine itself also has a sleep-promoting effect, effectively giving a “double boost.”

Guidelines for Athletes

Dosage:

• Daily recommended intake: 400-420mg for men, 310-320mg for women
• Supplemental dose: 200-400mg of elemental magnesium (be careful to distinguish elemental magnesium from the weight of the magnesium compound)
• Start with 200mg and gradually increase

Timing:

• 30-60 minutes before bed
• Can be taken with a small amount of food to reduce gastrointestinal discomfort

Side Effects:

• High doses may cause diarrhea (especially magnesium oxide and magnesium citrate)
• Caution is needed for those with poor kidney function
• May interact with certain medications

Additional Benefits for Athletes:

• Reduces the incidence of muscle cramps
• Improves post-exercise muscle soreness
• Supports electrolyte balance
• Assists in the recovery of glycogen storage

Glycine

What Is It?

Glycine is the simplest amino acid and also the main component of collagen. In recent years, it has attracted increasing attention in the field of sleep science.

Sleep Mechanism

Glycine’s sleep-promoting effect comes from an elegant mechanism — lowering core body temperature:

1. Glycine acts on NMDA receptors in the brain
2. Triggers peripheral vasodilation (especially at the extremities of the hands and feet)
3. Increases blood flow to the skin surface
4. Accelerates heat dissipation, lowering core body temperature
5. A drop in body temperature is a key trigger for falling asleep

In addition, glycine can also:

• Produce inhibitory effects at the spinal cord level, promoting muscle relaxation
• Act as a co-activator of GABA receptors
• Regulate the hypothalamic thermoregulatory center

Scientific Evidence

Multiple studies from Japan provide strong evidence:

• Sleep onset time: Shortens sleep latency
• Sleep quality: Both subjective and objective sleep quality improve
• Next-day performance: Subjects reported reduced fatigue, reduced daytime sleepiness, and improved cognitive performance the following day
• Deep sleep: Time to reach slow-wave sleep is shortened

One key study had subjects take 3g of glycine before bed, and the results showed significantly improved psychomotor test performance the next day, with an effect comparable to getting 1.5 extra hours of sleep.

Guidelines for Athletes

Dosage:

• 3 grams (3000mg) is the most commonly used and effective dose in studies
• Can be dissolved in warm water and drunk (mildly sweet taste)
• No need to cycle use; long-term use has a good safety profile

Timing:

• 30-60 minutes before bed
• Can be added to bedtime herbal tea

Side Effects:

• Very few reported side effects
• A small number of people may experience mild gastrointestinal discomfort at high doses
• One of the safest sleep supplements

Additional Benefits for Athletes:

• Glycine is a necessary component for collagen synthesis, aiding in tendon and ligament repair
• Involved in the synthesis of creatine (creatine = glycine + arginine + methionine)
• Has anti-inflammatory effects
• Supports liver detoxification function

Combination Strategy

Recommended “Sleep Stack”

Based on scientific evidence, the following combinations have been verified for both safety and effectiveness in athletes:

Daily Recovery Formula:

• Magnesium glycinate 200-400mg + Glycine 3g
• Taken 30-60 minutes before bed
• Can be used daily

Competition Period / Jet Lag Adjustment Formula:

• The daily formula above + Melatonin 0.5-1mg
• Limited to 3-5 days of use

Supplements Not Recommended

The following are some common but not recommended sleep products for athletes:

• Antihistamine sleep aids (such as diphenhydramine): Next-day residual effects impair reaction speed
• Alcohol: Severely disrupts sleep architecture, especially REM sleep
• CBD: Evidence is still insufficient, and some products may contain trace amounts of THC (doping risk)
• Oral GABA supplements: Oral GABA has difficulty crossing the blood-brain barrier, and its effectiveness is questionable

The Most Important Principle

Supplements are always a last resort, not the first choice. Before considering any supplement, please first ensure:

1. Your sleep hygiene habits are good (regular schedule, appropriate environment)
2. You do not have an undiagnosed sleep disorder (such as sleep apnea)
3. Your training load is reasonable (overtraining itself will disrupt sleep)
4. Your nutritional intake is balanced (getting nutrients from food is always better than supplements)

If you still need help after getting the basics right, magnesium and glycine are safe, science-backed starting points. Melatonin should be reserved for specific situations. Always consult a sports medicine professional before trying a new supplement.

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